1. Field of the Invention
The present invention relates to a Long Term Evolution (LTE) cell detecting apparatus in a multi-cell environment that may efficiently detect an LTE cell even in a multi-cell environment where interference occurs between adjacent cells.
2. Discussion of Related Art
FIG. 1 shows a configuration of a wireless frame of 10 ms in a Long Term Evolution (LTE) Frequency Division Duplexing (FDD) method. As shown in FIG. 1, in an LTE communication system, cell detection is performed by a synchronization signal (SS). Such an SS is divided again into a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), and each of the PSS and the SSS is transmitted twice per 10 ms at a time slot that is defined in advance.
Meanwhile, the LTE communication system has a total of 504 physical layer cell IDs to confirm the cell, the 504 physical layer cell IDs are divided again into 168 cell ID groups NID(1), and each of the groups is composed of 3 physical layer IDs NID(2). Accordingly, each of the cell groups includes 3 physical layer IDs such as 0, 1, and 2.
One of 504 physical layer cell IDs is allocated to each of the LTE cells so that the cell can be confirmed, and a terminal receives multiple LTE downlink signals in a wireless mobile communication environment, and therefore each of the physical layer cell IDs of the received LTE downlink signals should be detected to be used in network access, handover, and the like.
The following Equation 1 is a sequence for generating a PSS.
                                          d            u                    ⁡                      (            n            )                          =                  {                                                                      ⅇ                                                                                    -                        j                                            ⁢                                                                        π                          ⁢                                                                                                          ⁢                                                      un                            ⁡                                                          (                                                              n                                +                                1                                                            )                                                                                                      63                                                              ,                                                                                                                    n                    =                    0                                    ,                  1                  ,                  …                  ⁢                                                                          ,                  30                                                                                                      ⅇ                                                                                    -                        j                                            ⁢                                                                        π                          ⁢                                                                                                          ⁢                                                      u                            ⁡                                                          (                                                              n                                +                                1                                                            )                                                                                ⁢                                                      (                                                          n                              +                              2                                                        )                                                                          63                                                              ,                                                                                                                    n                    =                    31                                    ,                  32                  ,                  …                  ⁢                                                                          ,                  61                                                                                        [                  Equation          ⁢                                          ⁢          1                ]            
A conventional sequence du(n) for generating a PSS is generated as a Zadoff-chu sequence as shown in Equation 1, and a root sequence index u of the Zadoff-chu sequence is determined by a value of NID(2) as shown in the following Table 1.
TABLE 1NID(2)Root index u025129234
An SSS transmits 168 pieces of NID(1) information, and is composed of two m-sequences each having a length of 31 bits. The m-sequence having the length of 31 bits that defines the SSS is differently configured in a subframe 0 and a subframe 5 as shown in the following Equation 2.
                                              ⁢                              d            ⁡                          (                              2                ⁢                n                            )                                =                      {                                                                                                                                                                                    S                            0                                                          (                                                              m                                0                                                            )                                                                                ⁡                                                      (                            n                            )                                                                          ⁢                                                                              c                            0                                                    ⁡                                                      (                            n                            )                                                                                                                                                              in                        ⁢                                                                                                  ⁢                        subframe                        ⁢                                                                                                  ⁢                        0                                                                                                                                                                                                      S                            1                                                          (                                                              m                                1                                                            )                                                                                ⁡                                                      (                            n                            )                                                                          ⁢                                                                              c                            0                                                    ⁡                                                      (                            n                            )                                                                                                                                                              in                        ⁢                                                                                                  ⁢                        subframe                        ⁢                                                                                                  ⁢                        5                                                                                            ⁢                                                                  ⁢                                  d                  ⁡                                      (                                                                  2                        ⁢                        n                                            +                      1                                        )                                                              =                              {                                                                                                                                                          S                            1                                                          (                                                              m                                1                                                            )                                                                                ⁡                                                      (                            n                            )                                                                          ⁢                                                                              c                            1                                                    ⁡                                                      (                            n                            )                                                                          ⁢                                                                              Z                            1                                                          (                                                              m                                0                                                            )                                                                                ⁡                                                      (                            n                            )                                                                                                                                                              in                        ⁢                                                                                                  ⁢                        subframe                        ⁢                                                                                                  ⁢                        0                                                                                                                                                                                                      S                            0                                                          (                                                              m                                0                                                            )                                                                                ⁡                                                      (                            n                            )                                                                          ⁢                                                                              c                            1                                                    ⁡                                                      (                            n                            )                                                                          ⁢                                                                              Z                            1                                                          (                                                              m                                1                                                            )                                                                                ⁡                                                      (                            n                            )                                                                                                                                                              in                        ⁢                                                                                                  ⁢                        subframe                        ⁢                                                                                                  ⁢                        5                                                                                                                                                    [                  Equation          ⁢                                          ⁢          2                ]            
As can be seen from Equation 2, a plurality of two sequences S0(m0) and S1(m1) are determined by m0 and m1 determined by NID(1), and when m0 and m1 between adjacent cells are equal in a state in which a terminal receives a plurality of SSs, cell detection may be difficult due to increased interference.
In addition, when the terminal receives a plurality of SSSs, interference is increased due to characteristics of the m-sequence for generating the SSS, and therefore the detection performance of the cell is deteriorated.